Paul Schrader wrote the original script. After it was massively changed by Steven Spielberg, Schrader decided to remove his credit. Since the film couldn't be left with no credit for writing, Spielberg claimed it for himself.

Barry is shown to be surprised by the extraterrestrials. Director Steven Spielberg had two crewmembers hide in boxes off camera, one in a clown suit and one in a gorilla suit. One popped out, then the other as the cameras rolled, catching young Cary Guffey's bewildered reaction. Spielberg then whispered to the "gorilla" to remove his mask, eliciting a smile from Guffey.

SFX man Douglas Trumbull created the cloud effects by injecting white paint into tanks of salt and fresh water.

It is possible to see an upside down R2-D2 (from Star Wars (1977), etc.) in part of the large spacecraft that flies over Devil's Mountain. The SFX people needed more detail, and so supposedly there are many more such items, such as a shark from Jaws (1975) (also directed by Spielberg), etc. R2-D2 is visible as Jillian first sees the mothership up close from her hiding place in the rocks.

Spielberg and other producers wanted Walter Cronkite as newsreader for the broadcast that Neary ignores in the "living room sculpture" scene. However, CBS would not allow Cronkite to take the role, so producers settled on ABC's Howard K Smith. Unfortunately, the news cutaway scene to Wyoming reporter was filmed before this decision; as a result, the reporter says "Order your steak well-done, Walter."

Cary Guffey's performances were so good that they only ever had to do one or two takes of each shot he was in. He became known as "One-Take Cary" on the set, and Spielberg had a T-shirt printed up for him with the phrase written on it.